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How to Kill Brown Algae in Aquarium

Brown algae (or brown moss) scientifically known as Diatoms is one of the most common problems faced by many aquarists. Brown algae are in the form of plaque, brown patchy on rocks, driftwood, background, sand ... generally throughout the tank.

This brown algae shouldn't cause you any problems. Many experienced aquarists don't worry or get too concerned about brown algae and leave them alone, letting them disappear on their own.

These algae make the tank uncomfortable and can limit visibility to some extent, but this is no reason to panic and do all you can to prevent and eradicate it.

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1. What is brown algae?

In fact, there is a lot of confusing and conflicting information on the internet about this brown algae.

  • Some sources say that brown algae belong to the diverse class (Phaeophyceae), from small filaments to large and complex marine algae. According to the study, there are more than 1836 species in about 285 genera, and only less than 1% are found in freshwater habitats. However, 1% is more than 180 species of brown algae!
  • Other sources state that brown algae include the class Bacillariophyceae (with more than 16000 species ) is found in the world's oceans, rivers, lakes, and soils.

It is clear that in any case the casual aquarist cannot figure out the exact species of brown algae that may be present in the tank.

All brown algae have a distinct range of pH, salinity, light, temperature and water parameters where they will grow and develop. Therefore, the potential mix of species is extremely variable.

But we don't need to know that because the causes and treatments for brown algae are the same.

How to get rid of brown algae (diatoms) in freshwater tanks - on gravel

On the Internet, you can find many articles about brown algae in aquariums. In some of those articles you will find that the authors often mention that brown algae are not considered algae but some form of protozoa or bacteria.

Since then many aquarists believe this is why conventional algae treatments are not as effective for brown algae as products intended to "fix" algae problems.

Technically, this is not true.

In fact, brown algae are photosynthetic unicellular algae. 

Interesting facts: These algae are the only organisms on the planet whose cell walls are composed of transparent, colored silica.

2. How to recognize brown algae?

As the name implies, Brown algae in our tanks can be easily recognized from their small, round brown spots. Many of these brown spots are flat and hard. Also, they have a slimy feel. This can also be felt when you run your fingertips across its surface.

However, in science, the morphological determination of brown algae is based on the shape and structure of the valves and requires microscopic examination.

3. Is brown algae dangerous to shrimp, fish and plants?

The answer here is No, brown algae will not directly harm shrimps, fish and other animals and plants in your tank because brown algae are non-toxic.

How to get rid of brown algae (diatoms) in freshwater tanks - on plants

However, if the brown algae outbreak happens too quickly and strongly, it can have a number of negative effects, for example:

  • When brown algae cover plants, it can limit the rate of photosynthesis of plants. As a result, plants will not be able to absorb light and use it to convert carbon dioxide and water into glucose and oxygen. It will cause their growth to be stunted or in the worst case, the plant will die.
  • Brown algae growth is a sign of an unbalanced environment in the tank. If it starts to go bad, you need to pay attention to the shrimp. Shrimps require a good tank and stable water parameters to thrive. Sudden fluctuations will stress your shrimp.
  • Brown algae can deplete the oxygen in the tank if they die and decompose in large quantities.
  • This brown algae can cling to any hard surface in the tank, thus turning your tank into a brown mess.
Overall, while brown algae may not directly affect fish or shrimp, they can still inadvertently affect them through damage done to ornamental plants.

4. Causes of Brown Algae

If you have discovered brown algae in your tank and are looking for ways to prevent & stop them from growing then you may be wondering what causes brown algae and how diatoms get into your tank right away. from the beginning.

In fact, these algae eat silicates, nitrates and phosphate in water, the abundance of these compounds in your tank will cause them to grow rapidly.

Under conditions of sufficient nutrients and light, a diatom assemblage doubles almost every 24 hours through binary fission.

4.1. Silicate:

The presence of large amounts of silicate in your tank will definitely cause brown algae to appear. This is because brown algae use up all the silicates in the tank water to form their shells.

The silicate in your tank is mainly through the tap water, sand, and rock in the tank.

Brown algae prefer sand that hasn't been cleaned in a new tank. Always rinse clean sand, stones and test tap water or use or use RO water.

4.2. Nitrates:

Excess nitrate in the water can also accelerate the growth and spread of brown algae in the tank.

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According to research, the ratio of carbon:nitrogen:silicon:phosphorus in brown algae cells is on average 106:15:16:1. Therefore, brown algae need equal amounts of nitrogen and silicon to grow.

Nitrates occur naturally in any tank from waste, uneaten food, rotting plants, rotting driftwood, fertilizers,  dirty filter , etc

4.3. Phosphate:

Phosphorus is converted to orthophosphate and is available for use by all algae (not just brown algae) and other aquatic plants to grow.

Note : High phosphate levels can only contribute to brown algae growth in the tank. It is not the main reason for the appearance of brown algae.

Phosphates enter the tank system in many ways, such as: fish food, shrimp (especially frozen food), Animal waste, plant debris, chemical buffers (pH, KH) , aquarium salt, etc.

Brown algae in new and old aquariums

In the new tank. It's not surprising that almost all new aquariums go through the brown algae phase. This is completely normal. At this new tank stage, the new setups don't have many beneficial microorganisms to absorb and metabolize nitrogen.

As a result, brown algae benefit from reduced competition for nutrients and thrive in our tanks.

In the old tank. Brown algae don't appear out of nowhere. You must double-check all your steps. Did you change anything (tear up the substrate, add new fertilizer, use fish food, new shrimp, etc)? It may also be because you haven't done proper maintenance for too long (for example, your substrate or filter may require a thorough cleaning).

Sudden changes in tap water quality or seasonal changes can also lead to brown algae.

In general, when the tank is unbalanced and the water quality fluctuates, you can get brown algae.

5. How long can brown algae survive in an aquarium?

How to get rid of brown algae (diatoms) in freshwater tanks - on sand

If in a new tank, it can last until your tank is fully cycled and develops a balanced ecological system. Generally, it ranges from 4-6 weeks. When the nutrients are used up, the problem will resolve on its own.

As for the long-term stable tank, it can last from a few weeks to a few months. Why? Because everything depends on the abundance of nutrients in your water!

As long as the Brown algae have enough food, they will grow.

Note: As the brown algae begin to die, the color will fade. 

6. How to get rid of brown algae in the aquarium?

It's about creating stability in your aquarium. Therefore, you have two main options here:

  • Find the potential cause and act accordingly,
  • Let nature take its course. Eventually, the brown algae will disappear.
Importance: CANNOT get rid of brown algae completely. Even if the brown algae are no longer visible… there will always be some algae in any tank waiting for its time. It's completely natural so you shouldn't be too worried.

Removal of silicates using RO water:

The presence of silicates in aquariums is probably the main cause of brown algae. Brown algae have a special demand for silicates and are extremely effective at extracting them from water. 

Tap water often contains silicates due to the dissolution of the silicate minerals they come into contact with.

So, to avoid, remove silicate, we can use RO water for our aquarium.

Invest in a water purifier RO  are essential for your aquarium, thus removing silicates and other impurities that promote brown algae growth. Of course, it is possible to buy RO water bottles but in the long run it will be too expensive.

2. Manual removal:

This method is a proven way to get rid of brown algae as soon as they appear. It involves removing brown algae from surfaces by scrubbing or scraping them with special tools.

Here are some examples :

  • Toothbrush,
  • Soft filter pad,
  • rub pad,
  • glass scraper, etc.,

Gently scrape the tank walls and decorations until you have completely removed all visible traces of brown algae. Be very careful, you don't want these 'particles' floating in the water or clogging up the filter.

Read more: 50 best freshwater aquarium fish

Note : Be careful, if you have a  acrylic tank . You need to use special tools and blades that will not be able to scratch your tank glass.

If the diatoms get on the decorations, the old toothbrush will work just fine, really without the need for medication.

3. Water change:

Water exchange Regular use is one of the surefire ways to reduce brown algae growth.

By changing the water, the accumulation of excess nutrients (silicates, nitrates and phosphates) is prevented, encouraging brown algae to grow.

Attention : If you are using tap water for water change (not RO water), you need to know its parameters. In some places, tap water has a high silicate content. Depending on the season, there can also be some kind of fluctuation. So changing the water won't help.

In general, a weekly 20 – 30% water change is sufficient to keep the water free of excess inorganic compounds. However, in the event of a severe brown algae outbreak, up to 50% of water in the tank can be replaced.

Note : Be careful with the shrimp tank. Big water change  affect the molting process of shrimp .

4. Animals that eat algae:

Another way to control brown algae in an aquarium uses algae eaters.

Although this method is highly recommended by many aquarists, NuoiTep.Com recommends avoiding this option. Why?

  • If you have brown algae in your newly setup tank, it means the cycle isn't over yet. So the addition of certain types of fish, snails or shrimp can kill them. Only very healthy species should be placed in untreated tanks.
  • If you have brown algae in an old tank, it is likely that those algae eaters will refuse to eat the brown algae. Nutrient-poor brown algae. So when given a choice, animals will prefer something else.

However, if you're still thinking of adding an army of cleaners, here are the most popular brown algae eaters for aquariums:

Snails Note
Nerita snailNot recommended for new tanks
Fish ( sucker)Note
Otto fishNot recommended for new tanks
Pipa fishNot recommended for new tanks
Royal Farlowella Helicopter FishNot recommended for new tanks
Pencil FishNot recommended for new tanks
Hairy-nosed pikeNot recommended for new tanks
Neocaridina speciesNot recommended for new tanks
Caridina speciesNot recommended for new tanks

5. Chemical products (Phosphate and silicate removal products)

How to remove brown algae (diatom) in free water tank - Chemical products (phosphate and silicate removal products)

Many of these products are advertised as safe for fish and invertebrates. However, the use of chemicals to treat brown algae should be a last resort.

This is because we cannot control all of the potential effects of chemicals on the overall health of the aquarium.

For example, reducing phosphate to zero would be a huge mistake and inevitably lead to nutrient deficiencies for aquatic plants. If plants don't grow, they don't absorb nitrogen from the water. As a result, ammonia or nitrate spikes can kill your animal.

The most popular phosphate and silicate removal products:

  • Seachem Phosguard
  • Seachem PhosBond

Will CO2 help fight brown algae?

Generally yes. This process will not remove the algae on the spot, but will gradually inhibit its growth until it ceases to exist.

Increasing CO2 levels will also promote plant growth, thereby reducing the nutrients available in the tank for algae to grow. As a result, plants absorb nutrients much more efficiently, and eventually, they can outmaneuver brown algae.

You can increase your CO2 levels in two main ways:

  • CO2 injector pressurized CO2 tank.
  • Liquid Carbon, eg Seachem Flourish Excel, Easy Carbo.

Potential problems :

  • If you keep aquariums or fish in tanks and plan to use the CO2 method, I strongly recommend that you learn more about this topic. The addition of too much CO2 will cause the concentration of O 2 low (can cause suffocation) and the pH drops, which can also shock the animals in the tank.

Can a UV sterilizer be used against brown algae?

No, UV sterilizers are relatively useless against brown algae.

The problem is that all UV sterilizers are only effective against free-floating bacteria, algae, and other microorganisms that pass through the bulb.

Although, UV will kill some free-floating diatoms, once they attach to objects, they will have enough space to regenerate without getting close to UV rays.

Ways to prevent brown algae growth

  • Don't overfeed.
  • Don't overload.
  • Change water regularly.
  • Remove fish and shrimp leftovers and periodically vacuum the tank floor.
  • Quickly replace filter cartridges and filter cotton as needed.
  • Maintain proper stocking and feeding to prevent excess waste.
  • Regularly test the tank water with an accurate aquarium test kit to ensure that the water parameters (especially silicates) are at the proper level.


Brown algae are very common in new tanks. These algae are not difficult to control. It will usually go away on its own once the tank stabilizes (nitrogen balance). This is completely normal.

Brown algae can be easily prevented but if these algae are already thriving in your old tank, we can effectively control this problem by removing the nutrients needed for growth. grow and survive (silicates and phosphates). 

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